Streptococcus pneumoniae is an encapsulated bacterial pathogen that causes serious invasive diseases. Considerable evidence indicates that antibodies directed against the capsular polysaccharides mediate protection against pneumococcal infection. However, little is actually known about the clonal and molecular diversity of these important antibody specificities. Our experimental aims are to evaluate the clonality, variable region usage and functional properties of adult antibodies specific for the pneumococcal polysaccharide serotypes 6B, 14 and 23F.